Circadian disruption in flight performance primarily causes what change?

• A. Increases fatigue and reduces alertness.
• B. Increases alertness.
• C. No effect on performance.
• D. Improves reaction time.

Answer: (A)

Circadian disruption misaligns the body's internal clock with the external environment, leading to sleep loss and poorer sleep quality. That misalignment increases daytime sleepiness, lowers vigilance, and slows reaction time, all of which degrade flight performance. In practice, pilots or crew experiencing circadian disruption tend to be more fatigued and less alert, which is why the primary change is increased fatigue and reduced alertness. This does not boost alertness, nor does it leave performance unchanged or improve reaction time.